/*
 *  V4L2 video capture example
 *
 *  This program can be used and distributed without restrictions.
 *
 *  Originally found at: https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/capture.c.html
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>             /* getopt_long() */

#include <fcntl.h>              /* low-level i/o */
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#include <asm/types.h>          /* for videodev2.h */

#include <linux/videodev2.h>

#define CLEAR(x) memset (&(x), 0, sizeof (x))

typedef enum {
	IO_METHOD_READ,
	IO_METHOD_MMAP,
	IO_METHOD_USERPTR,
} io_method;

struct buffer {
	void *start;
	size_t length;
};

static char *dev_name = NULL;
static io_method io	= IO_METHOD_MMAP;
static int fd = -1;
struct buffer *buffers = NULL;
static unsigned int n_buffers = 0;

static void errno_exit(const char *s)
{
    fprintf (stderr, "%s error %d, %s\n",s, errno, strerror (errno));
	exit (EXIT_FAILURE);
}

static int xioctl(int fd, int request, void *arg)
{
        int r;
        do {
			r = ioctl(fd, request, arg)
		} while (-1 == r && EINTR == errno);
        
		return r;
}

static void process_image(const void *p)
{
	fputc ('.', stdout);
	fflush (stdout);
}

static int read_frame(void)
{
    struct v4l2_buffer buf;
	unsigned int i;

	switch (io) {
	case IO_METHOD_READ:
		if (-1 == read (fd, buffers[0].start, buffers[0].length)) {
			switch (errno) {
			case EAGAIN:
				return 0;
			case EIO:
				/* Could ignore EIO, see spec. */
				/* fall through */
			default:
				errno_exit ("read");
			}
		}
    	process_image (buffers[0].start);
		break;
	case IO_METHOD_MMAP:
		CLEAR (buf);

		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;

    	if (-1 == xioctl (fd, VIDIOC_DQBUF, &buf)) {
			switch (errno) {
			case EAGAIN:
					return 0;
			case EIO:
				/* Could ignore EIO, see spec. */
				/* fall through */
			default:
				errno_exit ("VIDIOC_DQBUF");
			}
		}

		assert (buf.index < n_buffers);

		process_image (buffers[buf.index].start);

		if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
			errno_exit ("VIDIOC_QBUF");

		break;
	case IO_METHOD_USERPTR:
		CLEAR (buf);

		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_USERPTR;

		if (-1 == xioctl (fd, VIDIOC_DQBUF, &buf)) {
			switch (errno) {
			case EAGAIN:
				return 0;
			case EIO:
				/* Could ignore EIO, see spec. */
				/* fall through */
			default:
				errno_exit ("VIDIOC_DQBUF");
			}
		}

		for (i = 0; i < n_buffers; ++i)
			if (buf.m.userptr == (unsigned long) buffers[i].start && buf.length == buffers[i].length)
				break;

		assert (i < n_buffers);

    	process_image ((void *) buf.m.userptr);

		if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
			errno_exit ("VIDIOC_QBUF");

		break;
	}

	return 1;
}

static void mainloop(void)
{
	unsigned int count;
    count = 100;

	while (count-- > 0) {
		for (;;) {
			fd_set fds;
			struct timeval tv;
			int r;

			FD_ZERO (&fds);
			FD_SET (fd, &fds);

			/* Timeout. */
			tv.tv_sec = 2;
			tv.tv_usec = 0;

			r = select (fd + 1, &fds, NULL, NULL, &tv);

			if (-1 == r) {
				if (EINTR == errno)
					continue;
				errno_exit ("select");
			}

			if (0 == r) {
				fprintf (stderr, "select timeout\n");
				exit (EXIT_FAILURE);
			}

			if (read_frame ())
				break;

		/* EAGAIN - continue select loop. */
		}
	}
}

static void stop_capturing(void)
{
    enum v4l2_buf_type type;

	switch (io) {
	case IO_METHOD_READ:
		/* Nothing to do. */
		break;
	case IO_METHOD_MMAP:
	case IO_METHOD_USERPTR:
		type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		if (-1 == xioctl (fd, VIDIOC_STREAMOFF, &type))
			errno_exit ("VIDIOC_STREAMOFF");

		break;
	}
}

static void start_capturing(void)
{

	unsigned int i;
	enum v4l2_buf_type type;

	switch (io) {
	case IO_METHOD_READ:
		/* Nothing to do. */
		break;
	case IO_METHOD_MMAP:
		for (i = 0; i < n_buffers; ++i) {
            struct v4l2_buffer buf;

			CLEAR (buf);

			buf.type	= V4L2_BUF_TYPE_VIDEO_CAPTURE;
			buf.memory	= V4L2_MEMORY_MMAP;
			buf.index	= i;

        	if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
				errno_exit ("VIDIOC_QBUF");
		}
		
		type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

		if (-1 == xioctl (fd, VIDIOC_STREAMON, &type))
			errno_exit ("VIDIOC_STREAMON");

		break;

	case IO_METHOD_USERPTR:
		for (i = 0; i < n_buffers; ++i) {
			struct v4l2_buffer buf;

			CLEAR (buf);

			buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
			buf.memory      = V4L2_MEMORY_USERPTR;
			buf.index       = i;
			buf.m.userptr	= (unsigned long) buffers[i].start;
			buf.length      = buffers[i].length;

			if (-1 == xioctl (fd, VIDIOC_QBUF, &buf))
				errno_exit ("VIDIOC_QBUF");
		}

		type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

		if (-1 == xioctl (fd, VIDIOC_STREAMON, &type))
			errno_exit ("VIDIOC_STREAMON");

		break;
	}
}

static void uninit_device(void)
{

	unsigned int i;

	switch (io) {
	case IO_METHOD_READ:
		free (buffers[0].start);
		break;

	case IO_METHOD_MMAP:
		for (i = 0; i < n_buffers; ++i)
			if (-1 == munmap (buffers[i].start, buffers[i].length))
				errno_exit ("munmap");
		break;

	case IO_METHOD_USERPTR:
		for (i = 0; i < n_buffers; ++i)
			free (buffers[i].start);
		break;
	}

	free (buffers);
}

static void init_read(unsigned int buffer_size)
{
	buffers = calloc (1, sizeof (*buffers));

	if (!buffers) {
		fprintf (stderr, "Out of memory\n");
		exit (EXIT_FAILURE);
	}

	buffers[0].length = buffer_size;
	buffers[0].start = malloc (buffer_size);

	if (!buffers[0].start) {
    	fprintf (stderr, "Out of memory\n");
        exit (EXIT_FAILURE);
	}
}

static void init_mmap(void)
{
	struct v4l2_requestbuffers req;

	CLEAR (req);

	req.count = 4;
	req.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_MMAP;

	if (-1 == xioctl (fd, VIDIOC_REQBUFS, &req)) {
		if (EINVAL == errno) {
			fprintf (stderr, "%s does not support memory mapping\n", dev_name);
			exit (EXIT_FAILURE);
		} else {
			errno_exit ("VIDIOC_REQBUFS");
		}
	}

	if (req.count < 2) {
			fprintf (stderr, "Insufficient buffer memory on %s\n",dev_name);
			exit (EXIT_FAILURE);
	}

	buffers = calloc (req.count, sizeof (*buffers));

	if (!buffers) {
		fprintf (stderr, "Out of memory\n");
		exit (EXIT_FAILURE);
	}

	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
		struct v4l2_buffer buf;

		CLEAR (buf);

		buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory      = V4L2_MEMORY_MMAP;
		buf.index       = n_buffers;

		if (-1 == xioctl (fd, VIDIOC_QUERYBUF, &buf))
			errno_exit ("VIDIOC_QUERYBUF");

		buffers[n_buffers].length = buf.length;
		buffers[n_buffers].start = mmap (NULL /* start anywhere */,
									buf.length,
									PROT_READ | PROT_WRITE /* required */,
									MAP_SHARED /* recommended */,
									fd, buf.m.offset);

		if (MAP_FAILED == buffers[n_buffers].start)
			errno_exit ("mmap");
	}
}

static void init_userp(unsigned int buffer_size)
{
	struct v4l2_requestbuffers req;
	unsigned int page_size;

	page_size = getpagesize ();
	buffer_size = (buffer_size + page_size - 1) & ~(page_size - 1);

	CLEAR (req);

	req.count = 4;
	req.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_USERPTR;

	if (-1 == xioctl (fd, VIDIOC_REQBUFS, &req)) {
		if (EINVAL == errno) {
			fprintf (stderr, "%s does not support user pointer i/o\n", dev_name);
			exit (EXIT_FAILURE);
		} else {
			errno_exit ("VIDIOC_REQBUFS");
		}
	}

	buffers = calloc (4, sizeof (*buffers));

	if (!buffers) {
		fprintf (stderr, "Out of memory\n");
		exit (EXIT_FAILURE);
	}

	for (n_buffers = 0; n_buffers < 4; ++n_buffers) {
		buffers[n_buffers].length = buffer_size;
		buffers[n_buffers].start = memalign (/* boundary */ page_size, buffer_size);

        if (!buffers[n_buffers].start) {
    		fprintf (stderr, "Out of memory\n");
            exit (EXIT_FAILURE);
			}
    }
}

static void init_device(void)
{
	struct v4l2_capability cap;
	struct v4l2_cropcap cropcap;
	struct v4l2_crop crop;
	struct v4l2_format fmt;
	unsigned int min;

	if (-1 == xioctl (fd, VIDIOC_QUERYCAP, &cap)) {
		if (EINVAL == errno) {
			fprintf (stderr, "%s is no V4L2 device\n", dev_name);
			exit (EXIT_FAILURE);
		} else {
			errno_exit ("VIDIOC_QUERYCAP");
		}
	}

	if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
		fprintf (stderr, "%s is no video capture device\n", dev_name);
		exit (EXIT_FAILURE);
	}

	switch (io) {
	case IO_METHOD_READ:
		if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
			fprintf (stderr, "%s does not support read i/o\n", dev_name);
			exit (EXIT_FAILURE);
		}
		break;
	case IO_METHOD_MMAP:
	case IO_METHOD_USERPTR:
		if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
			fprintf (stderr, "%s does not support streaming i/o\n", dev_name);
			exit (EXIT_FAILURE);
		}
		break;
	}

    /* Select video input, video standard and tune here. */
	CLEAR (cropcap);

	cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	if (0 == xioctl (fd, VIDIOC_CROPCAP, &cropcap)) {
		crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		crop.c = cropcap.defrect; /* reset to default */
		
		if (-1 == xioctl (fd, VIDIOC_S_CROP, &crop)) {
			switch (errno) {
			case EINVAL:
				/* Cropping not supported. */
				break;
			default:
				/* Errors ignored. */
				break;
			}
		}
	} else {	
		/* Errors ignored. */
	}

    CLEAR (fmt);

	fmt.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	fmt.fmt.pix.width       = 640; 
	fmt.fmt.pix.height      = 480;
	fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
	fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;

	if (-1 == xioctl (fd, VIDIOC_S_FMT, &fmt))
		errno_exit ("VIDIOC_S_FMT");

	/* Note VIDIOC_S_FMT may change width and height. */

	/* Buggy driver paranoia. */
	min = fmt.fmt.pix.width * 2;
	if (fmt.fmt.pix.bytesperline < min)
		fmt.fmt.pix.bytesperline = min;
	min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
	if (fmt.fmt.pix.sizeimage < min)
		fmt.fmt.pix.sizeimage = min;

	switch (io) {
	case IO_METHOD_READ:
		init_read (fmt.fmt.pix.sizeimage);
		break;
	case IO_METHOD_MMAP:
		init_mmap ();
		break;
	case IO_METHOD_USERPTR:
		init_userp (fmt.fmt.pix.sizeimage);
		break;
	}
}

static void close_device(void)
{
	if (-1 == close (fd))
		errno_exit ("close");

	fd = -1;
}

static void open_device(void)
{
	struct stat st; 

	if (-1 == stat (dev_name, &st)) {
		fprintf (stderr, "Cannot identify '%s': %d, %s\n", dev_name, errno, strerror (errno));
			exit (EXIT_FAILURE);
	}

	if (!S_ISCHR (st.st_mode)) {
		fprintf (stderr, "%s is no device\n", dev_name);
		exit (EXIT_FAILURE);
	}

	fd = open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);

	if (-1 == fd) {
		fprintf (stderr, "Cannot open '%s': %d, %s\n", dev_name, errno, strerror (errno));
		exit (EXIT_FAILURE);
	}
}

static void usage(FILE *fp, int argc, char **argv)
{
	fprintf (fp,
		"Usage: %s [options]\n\n"
		"Options:\n"
		"-d | --device name   Video device name [/dev/video]\n"
		"-h | --help          Print this message\n"
		"-m | --mmap          Use memory mapped buffers\n"
		"-r | --read          Use read() calls\n"
		"-u | --userp         Use application allocated buffers\n"
		"",
		argv[0]);
}

static const char short_options [] = "d:hmru";

static const struct option
long_options [] = {
        { "device",     required_argument,      NULL,           'd' },
        { "help",       no_argument,            NULL,           'h' },
        { "mmap",       no_argument,            NULL,           'm' },
        { "read",       no_argument,            NULL,           'r' },
        { "userp",      no_argument,            NULL,           'u' },
        { 0, 0, 0, 0 }
};

int main(int argc, char **argv)
{
	dev_name = "/dev/video";

	for (;;) {
		int index;
		int c;
		
		c = getopt_long (argc, argv, short_options, long_options, &index);

		if (-1 == c)
				break;

		switch (c) {
		case 0: /* getopt_long() flag */
			break;
		case 'd':
			dev_name = optarg;
			break;
		case 'h':
			usage (stdout, argc, argv);
			exit (EXIT_SUCCESS);
		case 'm':
			io = IO_METHOD_MMAP;
			break;
		case 'r':
			io = IO_METHOD_READ;
			break;
		case 'u':
			io = IO_METHOD_USERPTR;
			break;
		default:
			usage (stderr, argc, argv);
			exit (EXIT_FAILURE);
		}
	}

	open_device ();

	init_device ();

	start_capturing ();

	mainloop ();

	stop_capturing ();

	uninit_device ();

	close_device ();

	exit (EXIT_SUCCESS);

	return 0;
}
